Ultrasonic diagnosis allows to display in real time how the heart beats or the fetus moves, by simply bringing an ultrasonic probe into contact with the body surface. This technique is highly safe, and hence allows repetitive examination. Furthermore, this system is smaller in size than other diagnostic apparatuses such as X-ray, CT, and MRI apparatuses and can be moved to the bedside to be easily and conveniently used for examination. In addition, ultrasonic diagnosis is free from the influences of exposure using X-rays and the like, and hence can be used in obstetric treatment, treatment at home, and the like.
In addition, ultrasonic diagnosis is frequently used in the orthopedic field. For example, ultrasonic diagnosis is used to morphologically diagnose rheumatism and the rupture of tissues upon setting relatively fine tissues such as tendons, muscles, bones, and their surfaces as observation regions. The merit of the use of ultrasonic image diagnosis in the orthopedic field is that it is possible to not only grasp a change in fine structure as described above but also observe the movement of the structure in real time.
The image obtained by an ultrasonic diagnostic apparatus contains various kinds of noise and speckle caused by the interference phenomenon of received ultrasonic signals, which often hinder the accurate observation of the position and shape of the boundary of an object tissue, in addition to information associated with the object tissue. As an image filtering method of reducing such noise and speckle and enhancing information associated with an object tissue, there is available, for example, a method of detecting edge information of an image, smoothing information in the edge direction, and sharpening information in a direction perpendicular to the edge direction. In such a filtering method, when a tissue structure is almost uniform in a specific direction from the viewpoint of a local region like a muscle tissue structure, it is necessary to adjust the respective parameters of the filter so as to sharpen the structure.